March 27, 1903.J 



SCIENCE. 



487 



brain I hesitate to write a numerical series 

 for the total folds or segments of the fore- 

 brain, but with regard to the crucial point 

 in the investigation, the series and the 

 models seem to show conclusively that the 

 eye and its lens are morphologically ceph- 

 alad of the olfactory region of the brain 

 and of the nasal epithelium. 



A Preliminary Account of Studies on the 

 Japanese Frilled Shark, Chlamydosela- 

 chus: Bashford Dean, Columbia Uni- 

 versity. 



In view of the archaic features in the 

 adult, he noted as significant in the develop- 

 ment of this form the great depth of the 

 zone of yolk nuclei, the absence of external 

 gills, the more nearly terminal position of 

 the anus, the relatively smaller size of the 

 head, the enormous spiracular cleft and the 

 almost typically finfold type of limb. 

 Chlamydoselachus has specialized in the 

 line of producing large eggs, the largest 

 indeed among recent animals, ostrich 

 hardly excepted; that it was, however, un- 

 til recently an egg-depositing shark is ap- 

 parent from the character of the horn-like 

 capsule (with rudimentary tendriliform 

 processes) which the egg still retains. 



The Ependymal Grooves in the Roof of the 



Diencephalon of Vertebrates: Porter 



Edward Sargent. 



A cross-section of the brain of any of 

 the lower vertebrates in the region of the 

 posterior commissure reveals a character- 

 istic ependymal structure of conspicuous 

 form and size. In general this consists of 

 thickened and highly differentiated epen- 

 dyma forming a groove in the roof of the 

 diencephalon, extending from the posterior 

 commissure cephalad to the ganglia haben- 

 ulse. This has been mentioned by but four 

 writers, though it occurs in all vertebrates. 



In Petromyzon there are two grooves 

 located bilaterally on either side of the 



median plane. Posteriorly they converge 

 and extend about the posterior commis- 

 sural flexure and above it and are con- 

 tinued cephalad as two lateral horns of the 

 reeessus above the commissure. The 

 specialized ependyma of the grooves is 

 sharply marked off from the ependyma, 

 lining the other portions of the ventricle. 

 Nerve fibers from deep-lying cells pass be- 

 tween the cylindrical ependymal cells, and 

 into the ventricular groove. Here they 

 unite to form Reissner's fiber, the anterior 

 divisions of which lie within the groove. 



In the gnathostomes there is but one 

 median groove. In the skates, however, 

 the median groove bifurcates at either end, 

 —evidence of the persistence of the bi- 

 lateral condition. It is obvious that, 

 phylogenetically, the paired grooves of 

 cyclostomes have been crowded toward the 

 median plane by the development of lateral- 

 lying structures and fused to form the one 

 median groove. 



In ganoids, teleosts and amphibians the 

 ependymal groove is strictly median and 

 less conspicuous. It assumes a great 

 variety of forms in the different subgroups. 

 In reptiles it is much as in higher selach- 

 ians, but reduced in size. In birds it is 

 still further reduced. In mammals it has 

 become an inconspicuous structure, which 

 may still be recognized, however, in the 

 thickened ependyma just cephalad of the 

 posterior commissure. 



In general this ependymal structure acts 

 as a support for the constituent elements 

 of the fiber of Reissner, and as an 'an- 

 chorage ' for the fiber as a whole. 



On the Individuality of the Maternal and 

 Paternal Chromosomes in the Develop- 

 ment of the Hybrid between Fundulus 

 heteroclitus and Menidia notata: Wil- 

 liam J. MoENKHAUs, University of 

 Indiana. 

 Fundulus heteroclitus and 



